The market for 3D display devices is expanding. A difference in retinal images seen by both eyes (binocular disparity) that occurs when a user sees a 3D object by both eyes is produced in a display device, so that a 3D image can be displayed. 3D display devices using such binocular disparity with a variety of display methods have been developed and commercialized. Among such display devices, small display devices such as personal digital assistants or portable game machines mainly adopt a direct-view display method using an optical system such as a parallax barrier, a lenticular lens, or a microlens array.
For example, Patent Document 1 discloses a technique for displaying a 3D image by a parallax barrier so that a right eye sees an image for the right eye and a left eye sees an image for the left eye.